Your mentor was describing the acoustics of a cathedral, but the same doesn't work in the home where we don't have huge rooms to create those many seconds of reverberation. In a residential space we would get an echo chamber with muddled sound. Even in large churches these days there is the tradeoff between what the organist and choir prefer and the less reverberant acoustics required for intelligible speech.
In smaller rooms the choice is between a very dry acoustic with carpets and overstuffed furniture and a moderately reverberant space with hardwood or tile floors. I find that choice more a matter of preference with a bit of reverberation, all early reflections of course, perhaps being better for organ music.
There is frequently a problem getting a smooth bass response in rectangular rooms, especially reverberant rooms with dimensions that are multiples of each other. Don't expect the best results from a room that is 16' by 12' with an 8' ceiling. In this difficult room try to go with carpet and corner bass traps and add any lost sense of reverberant space with surround sound.
If there is a choice of rooms for the organ then look for the space with a vaulted ceiling, non-repetitive dimensions, and openings to adjacent rooms. The more irregular the dimensions the better off you are likely to be. My opinions only, I find this an interesting topic that affects all of us.